Combine png image with a background color for a shader
There are multiple options, but the easiest would be :


Put a hue/saturation/value node between your image texture and the principled BSDF, then tweak the hue to get the desired color.
Note : The downside is that you have to "guess" which hue you will get by tweaking the hue factor value.
Since your texture is black and white, you can use that as a mask to get the desired color. Insert a mix rgb node between the image texture and the bsdf, then tweak the Color2 input to get your color like so :

Note : You can disconnect the Color1 input from the mix RGB node and set any color you wish for the numbers.
You can also use a mix shader and use the color for the factor, that way you can have a different roughness value for the numbers and the rest of the clock for example. I have used diffuse shaders for the sake of simplicity but you can use Principled bsdfs :


Edit :
Since your image may not be exactly black and white, it could mess up the masking factor. I'd recommend inserting a color ramp, setting it to "constant" and moving the white slider to 0.5 like so :